Devices of this type are not new per se. For example, a typical prior art device is shown in West German Offenlegungsschrift No. 3,333,66. The assembly device shown in this patent serves to press or fit universal joint bearings into the bore of the universal joint. For this purpose, the joint cross is either separately introduced and held in position or it can already be a component of a universal joint shaft or the like. It has been found that during the assembly process, it is important to maintain the center offset of the joint parts relative to each other as small as possible. Center offsets are a problem which cannot be corrected after assembly of the parts. It has been found that different pressing forces resulting from production tolerances of the universal joint bearings and the bores or different cross sections and structural differences in the fork arms can cause the center offsets. The prior known device incorporates means for correction. However, it is noted that there are areas in which the assembly results can be improved even further.
In the prior known devices, the pressing and fitting of the universal joint bearings into place is carried out with a hydraulic work cylinder. The requisite pressure for actuating the cylinder is provided by a pressure generator and a valve which allows the required amount of pressure medium to flow into or out of the work chamber of the work cylinder as needed. The pressure generator provides a pressure which is always more than the required value. The value is controlled as a function of the measurement value obtained from the center offset described above and continually regulates during the pressing and/or fitting process, the amount of pressure medium present in the work chamber of the work cylinder. The high force required especially when the universal joint bearing is being fitted is available even at minimal travel of the piston or of the fitting ram attached to it. It has been found that when extremely short travels are reuired, particularly at the end of the assembly process, which are in the range of 0.1 to 0.01 mm, a more sensitive quantity control by the flow control valve can lead to even better results. It has been found that a particularly critical situation is encountered when, at the end of the fitting process in one of the joint forks, too much pressure medium is supplied by the valve to the work chamber, even if this excess is very small. A center offset caused in this way leads to isolated cases of assembly results which, even though the overall results are considered satisfactory are still outside the field of tolerances for the amount of center offset.